A quadrilateral has three angles which measure 23.5 degrees, 99 degree, and 100.4 degrees. What is the measure of the fourth angle?

Quadrilaterals always have a total of 360°. Because of this fact, we can find the 4th angle by subtracting 23.5, 99, and 100.4 from 360. This is equal to 360 - (23.5 + 99 + 100.4) = 137.1. So, the fourth angle is 137.1°.

I think it would be 137.1, due to the total being 360. Just subtract.